Roll end relief for rolling mills

ABSTRACT

A roll for a rolling mill, the roll having end reliefs that reduce substantially roll end spalling and increase substantially the range of roll contour control by roll bending. The end reliefs of the roll comprise two symmetrically located, smoothly curving exponential functions extending either (1) from the center line of the roll face to the two ends of the roll, or (2) from two locations intermediate the ends of the roll and the roll face center line to the ends of the roll.

D e Elnateel gtates Paeene n w 1111 3,7333% Anderson et al. [4 1 May 22,R973 [54] ROLL END RELIEF FOR ROLLING 1,895,607 1 1933 Coe ..72 241MILLS 3,545,239 12/1970 Kennedy ..72/10 [75] inventors: Arvid N.Anderson; Richard H. Batterman" both of New Kensington, PrzmaryExaminer-Milton S. Mehr p Attorney--Elroy Strickland [73] Assignee:Aluminum Company of America,

Pittsburgh, Pa. [57] ABSTRACT A roll for a rolling mill, the roll havingend reliefs that [22] Filed 1971 reduce substantially roll end spallingand increase sub- [21] Appl. No.: 190,902 stantially the range of rollcontour control by roll bending. The end reliefs of the roll comprisetwo sym- 52 us. c1 ..72/241, 29/115 metrically located. smoothly curvingexponential fune- [51] Int. Cl. ..B21h 27/00 tiens extending either fromthe center line of the [58] Field of Search 72/241, 199, 245, roll faceto the two ends of the roll, or (2) from two 72/237; 29/1 10, 115locations intermediate the ends of the roll and the roll face centerline to the ends of the roll. [56] References Cited 7 Claims, 3 DrawingFigures UNITED STATES PATENTS 3,334,506 8/1967 Hicks ..72/245 X & 6 C 17m i I PAIENTEL MAY22I975 FIG. 2.

BEVELLED REL/EF CURVED RELIEF l 25 DISTANCE FROM CENTERL/NE IN INCHES 30v END ROLL END RELIEF FOR ROLLING MILLS BACKGROUND OF THE INVENTION Thepresent invention relates generally to rolls for rolling mills, andparticularly to end reliefs for work and/or back-up rolls.

In four-high and other types of rolling mills employing back-up rolls,the ends of the back-up or work rolls are usually provided with atapered relief to reduce peak contact pressure between the work andback-up rolls, which tends to concentrate at the ends, in an effort toreduce spalling of the ends of the work and back-up rolls.Parenthetically, spalling is a failure of the roll surface under theforce of rolling loads, with pieces of the surface actually comingloose. The spalled roll is often damaged severely and may requirereplacement. Other detrimental considerations include the dangerinvolved in spall pieces that may fly off the rolls, and possible damageto cooperating work or back-up rolls, and to the sheet being rolled.

Roll spalling, however, has remained a problem even with tapered endreliefs. The primary reason for this has been that of the nature of thetapers themselves. Heretofore, tapers have been straight, lined orbevelled so that the bevelled portion of the roll met an intermediatecylindrical or curved portion of the roll to form a fairly well defined,annular crease or edge on the roll surface, i.e., the bevelled ends andthe cylindrical or curve surface of the intermediate portion of the rollforms a rather abrupt change of direction on the roll surface eventhough the angle of the bevel is slight. Thus, even though the bevelledend relief is designed and does tend to reduce spalling by distributingsomewhat the contact pressure between the work and back up rolls, theedge formed by the change of directions between the intermediate andbevelled end portions of the roll creates high peak pressures betweenthe work and the back-up rolls at the location of the edge. These highpeak pressures have been found to be surprisingly high, as discussedhereinafter, and are the primary cause of continued spalling of the rollends.

In addition to the problem of roll spalling, better asrolled sheetflatness has been a long sought after goal in the sheet rolling art. Theflatness of a sheet being rolled is determined by the contour of the gapbetween the work rolls, which contour is controlled partly by controlledbending of the work rolls. Controlled bending of the work rolls may beaccomplished by use of roll separating jacks and reverse jacks operatingon the necks of the work rolls. The effectiveness of the roll jacks incontrolling the roll gap contour is directly affected by the degree andextent of the taper of the roll end reliefs. The effectiveness of thejacks is maximized by allowing only point contact between the work andback-up roll at the center of the face of the rolls, i.e., at the centerof the rolling mill. Such a roll contour, however, would lead toprohibitively high stresses at the point of contact so that a compromisesolution is required and desired to maximize jack effectiveness whilesimultaneously minimizing roll contact pressures to avoid spalling.

BRIEF SUMMARY OF THE INVENTION The present invention provides such acompromise by using a smoothly curving, exponential function for thecontour of back-up or work rolls, which contour provides end reliefwithout an annular edge or crease on the roll surface to cause rollspalling, while simultaneously increasing the length of the taper toprovide increased jack effectiveness. In addition, such a function iseasily employed in the process of making the roll. For example, it canbe used to control roll grinding machines which provide the roll surfacewith a particular, finished contour.

For rolls requiring a contour other than convex (e.g., flat or concave),a compound curve may be used, and in this case the curves of the endreliefs and the curve of the center or intermediate portion of the rollface will intersect at two locations intermediate the ends of the rolls.The slopes of curves of the end reliefs, as provided by the exponentialfunction, and the slope of the curve of the center portion of the rollare equal to zero at the two intersecting locations, as explained morefully hereinafter.

THE DRAWING The invention, along with its advantages and objectives,will best be understood from the following detailed description inconnection with the accompanying drawing in which:

FIG. 1 is a schematic end view representation of a single stand of atypical four-high rolling mill;

FIG. 2 is a diagram showing one half of the roll face of a back-up rollprovided with the end relief of the present invention, and astraight-line, bevelled end relief shown in dash outline;

FIG. 3 is a graph illustrating contact pressures between a work roll andthe back-up roll of FIG. 2.

PREFERRED EMBODIMENT Referring now to the drawing, FIG. 1 showsschematically a typical four-high stand of a rolling mill 10 in whichupper and lower back-up rolls l1 and 12 are located to roll against twowork rolls 13 and 14 in a process of reducing the thickness of a sheetof metal 15 traveling between the work rolls.

As explained earlier, the rolling force between the work and back-uprolls tended to concentrate at the edges and ends of the rolls thatresulted in spalling of the roll ends. In an effort to correct thisproblem, the ends of the back-up (or work) roll were provided (ground)with a straight line taper, as indicated in FIG. 2 by dash outline 16 atone end of the upper back-up roll 11. Only one half of one back-up rollis shown in FIG. 2 since the other half, as well as the lower back-uproll 12, would have essentially the same end configurations. The taperl6 joins the intermediate portion 17 of the roll face at a location 18to provide the roll with an essentially bilinear contour.

From a roll deformation program derived analytically, i.e., bycalculations involving principles of mechanics, it has been found thatextremely high peak pressures exist between the work and back-up rollswhere the taper relief 16 joins the generally flat portion 17 of theroll grind, i.e., at the region or location 18 on the roll face. Thishigh peak pressure is caused by an annular edge or crease at thelocation 18 where, as explained above, the tapered and intermediateportions of the roll face change directions. In FIG. 3 this peakpressure is shown by dash line curve 20 for a 38 inch diameter, 60 inchlong back-up roll employed in a mill for cold rolling aluminum andaluminum alloy sheet. The curve 20 is a plot of roll pressure in kipsper inch against the distance from the center line of the mill and theroll 11 of FIG. 2. At the end of the roll, the pressure line 20 drops tozero since the taper removes essentially all pressure between the tworolls at their ends. However, as seen in FIG. 3, in moving away from theroll end and toward the roll face center line, the pressure risesrapidly to a point approaching 70 kips per inch in comparison to a 27 to29 kips per inch range for the remainder of the distance to the rollface center line. This peak pressure point corresponds distance-wise (inreference to the roll face center line) to the location or edge 18 onthe roll face. It is this high peak pressure at 18 that is the primarycause of continued roll spalling in the rolling art.

In accordance with the present invention, the backup rolls and/or thework rolls of a rolling mill are provided with a smoothly curving,exponential function extending from the ends of each roll to an originat (l) the center line of the roll face for a roll having a crownconsisting entirely of the exponential curve, or at (2) two locationsintermediate the roll face center line and the ends of the roll having acompound crown consisting of an arbitrary central contour blending withthe exponential end relief. Such a smoothly curving, exponentialfunction blends optimumly the end reliefs and the intermediate portionof the rolls to eliminate the annular edge 18, and thus the peakpressures and the roll spalling resulting therefrom. The reduction inpeak pressure is illustrated by the solid line 22 in FIG. 3. In goingfrom the center line of the mill to the end of the roll, only a slightrise in roll pressure occurs before pressure falls to zero at the veryend of the roll.

The exponential function providing such advantageous results may bedefined for the special case (1) above by the equation where, as shownin FIG. 2, x is any selected distance from the center line of the milland roll face y is the relief at x c is the maximum relief at the rollends L is the length of the roll, and

n is the exponent.

Rolls provided with the above exponential function and used in rollingmills to roll metal sheet have demonstrated their effectiveness insubstantially reducing roll end spalling.

In addition, it can be demonstrated that for any bevel relief of anamount c over a'length B (with B being the distance from the roll end tolocation 18 on the roll face shown in FIG. 2) the effectiveness of workroll separating jacks in controlling the gap between the work rolls byroll bending and thus control of as-rolled sheet flatness, is improvedby using the above equation with n L/2B, with n being greater than one.This value of n produces a curve which is tangent to the bilinearcontour of the roll face as depicted in dash outline in FIG. 2. Asreadily seen, for the same amount of maximum end relief c, the back-uproll 11 with the curved function contacts the work roll at a locationinwardly of the contact point 18 of the bevelled roll. This increasesthe distance that the work roll end is free of the back-up roll toprovide greater leverage for the roll bending process.

With roll contours corresponding to case (1) above, the magnitude of theterm x (in the above formula) at the center line of the mill is, ofcourse, zero, and the slope of the curve at the center line is thus zeroor flat.

In going from the center line toward the ends of the roll, which is alinear progression, the magnitude of x increases gradually andincrementally from zero, by finite numbers in measurement of theprogression, to provide a roll with a convex shape.

However, with roll contours corresponding to case (2) above, the curveof the end relief provided by the present invention will intersect thecurve of an intermediate or center portion of the roll, having thecylindrical or concave configuration, at two locations intermediate theends of the rolls. At these two intersecting locations, the curve of theend relief exponential function begins with a zero or flat slope sincethe distance x originates at the intersecting locations rather than thecenter line of the mill.

As can be appreciated, jack effectiveness for the bending process ismaximized by allowing only point contact between the work and back-uprolls at the center of the mill. Such a roll contour, however, wouldlead to extremely high stresses at the point of contact as explainedearlier. The smoothly curving, exponential function of the presentinvention provides a compromise between the two by providing a verygradual decrease in contact pressure between the work and backup rollsalong a major portion of their length, for a roll having a convex crown,with relief increasing to a maximum more rapidly, though yet gradually,in its approach to the ends of the back-up roll. In this manner, theproblem of high stress points, with resulting spalling, is essentiallyeliminated while simultaneously increasing jack effectiveness forincreased control of roll bending to provide better as-rolled sheetflatness.

For rolls having an essentially straight cylindrical shape, or a concaveconfiguration, the effect of the exponential function of the inventionis the same, i.e., the function blends the end reliefs with theintermediate portion of the roll face to remove high stress points onthe roll face and to increase jack effectiveness by increasing thedistance of end relief.

While the invention has been described in terms of preferredembodiments, the claims appended hereto are intended to encompass allembodiments which fall within the spirit of the invention.

Having thus described our invention and certain embodiments thereof, weclaim:

1. A roll for a rolling mill having end reliefs comprised of twosmoothly curving exponential functions extending from the roll facecenter line to both ends of the roll, with the slope of the curve of theroll face at the center line being zero, and increasing in magnitudetoward the ends of the roll from said center line.

2. The roll of claim 1 in which the exponential function is defined bythe equation x is any selected distance from the center line of the milly is the relief at x c is the maximum relief at the roll ends L is thelength of the back-up rolls, and

n is an exponent.

3. The roll of claim 2 in which the exponent n is greater than one.

4. A roll for a rolling mill having a center portion provided with apredetermined configuration or curve and an end relief adjacent each endof the roll, with each end relief comprising a smoothly curving,exponential function, and intersecting the center portion of the roll attwo locations intermediate the roll face center line and the ends of theroll, the slopes of the curves of the end reliefs increasing in thedirection of the roll ends from said intermediate locations, with thecurves of the end reliefs and the curve of the intermediate portion atthe two intersecting locations having slopes equal to zero.

5. In a rolling mill having work and back-up rolls, with at least one ofthe rolls having end reliefs comprised of two symmetrically located,smoothly curving, exponential functions extending from the roll facecenter line to both ends of the roll, with the slopes of the curvesincreasing in the direction of the roll ends from nential functions.

1. A roll for a rolling mill having end reliefs comprised of twosmoothly curving exponential functions extending from the roll facecenter line to both ends of the roll, with the slope of the curve of theroll face at the center line being zero, and increasing in magnitudetoward the ends of the roll from said center line.
 2. The roll of claim1 in which the exponential function is defined by the equation y c((2x)n/L ) where x is any selected distance from the center line of themill y is the relief at x c is the maximum relief at the roll ends L isthe length of the back-up rolls, and n is an exponent.
 3. The roll ofclaim 2 in which the exponent n is greater than one.
 4. A roll for arolling mill having a center portion provided with a predeterminedconfiguration or curve and an end relief adjacent each end of the roll,with each end relief comprising a smoothly curving, exponentialfunction, and intersecting the center portion of the roll at twolocations intermediate the roll face center line and the ends of theroll, the slopes of the curves of the end reliefs increasing in thedirection of the roll ends from said intermediate locations, with thecurves of the end reliefs and the curve of the intermediate portion atthe two intersecting locations having slopes equal to zero.
 5. In arolling mill having work and back-up rolls, with at least one of therolls having end reliefs comprised of two symmetrically located,smoothly curving, exponential functions extending from the roll facecenter line to both ends of the roll, with the slopes of the curvesincreasing in the direction of the roll ends from said center line, thesmoothly curving, exponential functions being effective to reducesubstantially the tendency of the work and back-up rolls to spall underthe force of rolling loads, while simultaneously accommodating anincreased range of roll contour control by roll bending.
 6. The mill ofclaim 5 in which the back-up rolls have end reliefs comprised of thesmoothly curving, exponential functions.
 7. The mill of claim 5 in whichthe work rolls have end reliefs comprised of the smoothly curving,exponential functions.